Various devices have been developed for holding material or materials in registration during the sewing process. These devices are typically designed for specific applications, such as for the sewing of pockets or cuffs on shirts, collars on jackets, or for the monogramming of ties, etc. Such devices improve registration accuracy, but it has been determined that the time required for loading and unloading the material or materials into the device can equal or exceed the time required for the actual sewing process. Because of this, considerable effort has been directed to developing clamps and/or pallets which can accommodate multiple pieces of material to be sewn. By accommodating multiple pieces of material, the ratio of the time required for loading and unloading the material versus the actual sewing time is substantially reduced. However, it has been found that even though the use of clamps or pallets reduces the foregoing ratio and thus increases productivity, it creates other problems with respect to maintaining registration of the material during the sewing process and adapting the clamp or pallet to the sewing machine involved.
In order to maintain precise registration of the material or materials within the clamp or pallet, a sufficient clamping force must be applied to the material or materials and this force must be substantially uniform around the periphery thereof. However, during the sewing process, the sewing machine imposes various forces on the material or materials which can impair registration unless a sufficient uniform clamping force is maintained. For example, when the needle is being withdrawn from the material or during stitch setting, the material is pulled upwardly away from the throat plate of the sewing machine. Also, the actual sewing process imposes a horizontal force on the material in the direction of sewing. Furthermore, some sewing systems actually feed the material continuously which results in the material being moved when the needle is still in the material. It has been found that the clamps and pallets presently available do not provide a sufficient clamping force on the material or materials to overcome the foregoing forces, and thus registration of the material or materials during the sewing process is virtually impossible to maintain.
Due to the wide variety of sewing machines available, the clamp or pallet must be designed so as to be readily adaptable to most machines. However, conventional sewing machines have design limitations with respect to the height of the needle and the presser foot, and the size of the underarm space. The foregoing parameters limit the size, shape and overall height of the clamp or pallet, particularly when in the closed position. Here again, it has been found that the design of clamps and pallets presently available is such that they are not easily adaptable to many sewing machines, thus preventing the use of the clamps or pallets with such machines.
Because of the foregoing, it has become desirable to develop a clamping device which can retain a multiplicity of pieces of material in registration during the sewing process, and which is easily adaptable for use with a wide range of sewing machines.